CN113285620A - Multi-alternating-current port modular multi-level converter and control method thereof - Google Patents

Multi-alternating-current port modular multi-level converter and control method thereof Download PDF

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CN113285620A
CN113285620A CN202110714164.0A CN202110714164A CN113285620A CN 113285620 A CN113285620 A CN 113285620A CN 202110714164 A CN202110714164 A CN 202110714164A CN 113285620 A CN113285620 A CN 113285620A
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converter
voltage
phase
port
current
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CN113285620B (en
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张建文
孙勇
冯欣
施刚
周剑桥
蔡旭
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/483—Converters with outputs that each can have more than two voltages levels
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/02—Circuit arrangements for ac mains or ac distribution networks using a single network for simultaneous distribution of power at different frequencies; using a single network for simultaneous distribution of ac power and of dc power
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/04—Circuit arrangements for ac mains or ac distribution networks for connecting networks of the same frequency but supplied from different sources
    • H02J3/06—Controlling transfer of power between connected networks; Controlling sharing of load between connected networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/36—Arrangements for transfer of electric power between ac networks via a high-tension dc link
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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Abstract

The invention discloses a multi-alternating current port modular multilevel converter and a control method thereof, wherein the multi-alternating current port modular multilevel converter comprises the following steps: a modular multilevel converter; and a multi-port flexible interconnect module in series with the modular multilevel converter. The invention can realize interconnection of a plurality of alternating current lines and a direct current power grid in a station of the same converter station and active control of alternating current line power flow; compared with the existing common networking structure of the AC/DC converter station, the networking structure of the AC/DC converter station adopts a transformerless structure, adopts a mode of simultaneously feeding a plurality of AC lines and an AC/DC power grid interconnection mode, and has great advantages in the aspects of power density, converter station size, construction cost, power supply reliability, power supply system operation efficiency and the like; the flexible interconnection of the multiple alternating current lines is realized by utilizing the multi-terminal flexible interconnection module, the flexible interconnection has the characteristic of modularization, and the port expansion of the alternating current lines can be economically, efficiently and conveniently realized by increasing the number of the first single-phase converters in the interconnection module.

Description

Multi-alternating-current port modular multi-level converter and control method thereof
Technical Field
The invention relates to the technical field of medium-high voltage alternating current and direct current hybrid power grids, alternating current and direct current converter station networking structures and power electronics, in particular to a multi-alternating current port modular multilevel converter and a control method thereof.
Background
The ac/dc hybrid power grid is gradually becoming a hot spot of domestic and foreign research by virtue of its advantages in power supply capacity, power supply reliability, power quality, system flexibility, and the like. The AC-DC converter station is a link for connecting a DC power grid and an AC power grid, the power electronic converter is used as core equipment in the AC-DC converter station, is usually a Voltage Source Converter (VSC) and can be divided into a two-level topology, a three-level topology and a modular multilevel topology, the converters of the two-level and the three-level topologies have simple structure and mature technology, but a large number of IGBTs are required to be connected in series for use in medium-high voltage occasions, so that the voltage-sharing problem is brought, and only one company ABB can solve the problem at present; meanwhile, in order to obtain better dynamic characteristics and harmonic characteristics, the two-level and three-level converters need high-frequency switching, so that the switching loss is larger; the Modular Multilevel Converter (MMC) topological structure adopts a submodule cascading mode, reduces the requirement on the voltage-resistant grade of a device, and has remarkable advantages in manufacturing difficulty, switching loss, waveform quality and fault handling capacity, so that the MMC topological structure is more suitable for application in medium-high voltage occasions. In addition, the networking structure of the ac/dc converter station may affect various aspects such as system cost, power supply reliability, protection configuration, and control flexibility, and providing a method may meet application requirements such as low cost and high power density on the basis of realizing the function of multiple ac lines is a problem to be solved urgently.
Disclosure of Invention
This section is for the purpose of summarizing some aspects of embodiments of the invention and to briefly introduce some preferred embodiments. In this section, as well as in the abstract and the title of the invention of this application, simplifications or omissions may be made to avoid obscuring the purpose of the section, the abstract and the title, and such simplifications or omissions are not intended to limit the scope of the invention.
The present invention has been made in view of the above-mentioned conventional problems.
Therefore, the technical problem solved by the invention is as follows: the existing networking structure of the AC/DC converter station can only realize the feed-in of a single AC line and does not have the functions of interconnection of a plurality of AC lines and active power flow decoupling control of the AC/DC lines.
In order to solve the technical problems, the invention provides the following technical scheme: a modular multilevel converter; and a multi-port flexible interconnect module in series with the modular multilevel converter.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the modular multilevel converter comprises a medium-high voltage level voltage source type converter.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the multi-port flexible interconnection module comprises a plurality of first single-phase converters connected in parallel on a common connecting bus, and an alternating current output port of each single-phase converter is connected with a corresponding alternating current line.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the modular multilevel converter submodule topology comprises a half-bridge submodule topology, a full-bridge submodule topology, a clamping type dual-submodule topology or a topology formed by multiple structures in a mixed connection mode.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the common connection bus comprises a medium and low voltage direct current bus, and a common connection capacitor connected with the medium and low voltage direct current bus provides voltage for the medium and low voltage direct current bus.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the multi-port flexible interconnection module is divided into three schemes according to the fact whether a second single-phase converter is contained or not, the contained second single-phase converter is different from the wiring modes of the upper bridge arm and the lower bridge arm of the modular multilevel converter, and the schemes comprise that scheme 1: the multi-port flexible interconnection module does not comprise the second single-phase converter, and alternating current output ports of an upper bridge arm and a lower bridge arm of the modular multi-level converter are respectively connected with a positive pole and a negative pole of a common direct current bus of the multi-port flexible interconnection module; scheme 2: the multi-port flexible interconnection module comprises a second single-phase converter which is connected with the first single-phase converter in parallel at two ends of a common direct-current bus, and an alternating-current port of the modular multilevel converter is connected with an alternating-current output port of the second single-phase converter; scheme 3: the flexible interconnection module of multiport contains first single-phase transverter and two single-phase transverters of second with alternating current line quantity matching, first single-phase transverter and two single-phase transverters of second connect in parallel at public direct current bus both ends, the AC output port of two single-phase transverters of second respectively with the AC output port of the upper and lower bridge arm of modularization multi-level transverter links to each other.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the first single-phase converter and the second single-phase converter comprise voltage source type single-phase converters.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the topology of the first single-phase converter or the second single-phase converter in the multi-port flexible interconnection module comprises a two-level half-bridge converter, a three-level half-bridge converter or a single-phase bridge converter capable of performing power bidirectional flow.
As a preferable solution of the multi ac port modular multilevel converter according to the present invention, wherein: the output voltage of a port of a single-phase converter in the multi-terminal flexible interconnection module comprises direct current components with the same size and different alternating current components obtained by control according to requirements; and the direct-current component of the voltage of the output port of the single-phase converter is half of the voltage value of the public connection bus.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the method comprises alternating current line power flow control, modular multilevel converter control and common direct current bus voltage balance control.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the multi-end flexible interconnection module and the modular multilevel converter flexibly interconnect a plurality of alternating current lines and a direct current power grid through cooperative control, and adjust the power flow distribution on the lines; when the multi-section flexible interconnection module is interconnected with n AC lines, the power flow P on each AC line is adjusted1～PnAnd Q1～QnAnd DC side load power PLControlling, wherein the active power of one AC line is automatically adjusted through the energy balance of the system, only the reactive power on the line is controlled, and the AC line is defined as an AC line 1; in the control, the three-phase alternating current component locked by the phase-locked loop is the three-phase node voltage of the alternating current line 1 controlled by the constant reactive power, and the voltage current under the three-phase alternating current a-b-c coordinate system is converted into a d-q coordinate system through Park conversion for active and reactive component decoupling control through the phase of the real-time output power grid voltage.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the AC line power flow control comprises a voltage v at a node 1 of the line 1, based on the AC line 11jNode voltage v to line kkjAnd converting the dynamic equation into a d-q coordinate system to obtain the following equation:
Figure BDA0003134163460000031
wherein, V1d、V1q、Vkd、Vkq、I1d、I1q、Ikd、IkqD-q axis components, L, of line 1 and line k node voltage currents, respectively1、R1、Lk、RkThe inductance and the equivalent resistance on the line 1 and the line k respectively, omega represents the angular frequency of the power grid, delta Uc1kd、ΔUc1kdIs an equivalent voltage Deltauc1kj＝uc1j-uckjD-q axis component of (u)c1jIs the AC component of the output voltage of a first single-phase converter connected to an AC line 1ckjJ is a, b, c, an ac component of the output voltage of the first single-phase converter connected to the ac line k.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the method further comprises the step of carrying out closed-loop control on the current on the line k by using a PI controller, wherein a specific control equation is as follows:
Figure BDA0003134163460000041
wherein the superscripts denote reference values, k, of the respective componentspkAnd kikProportional and integral coefficients, V, of a power flow control loop PI regulator of line k, respectively1d、V1q、Vkd、VkqFor the feed-forward term,. omega.L1I1d、ωL1I1q、ωLkIkd、ωLkIkqIs a feedforward decoupling term;
a d-axis component reference value of a line current of the AC line power flow control loop
Figure BDA0003134163460000042
And q-axis component reference value
Figure BDA0003134163460000043
Reference value of active power according to ac line k
Figure BDA0003134163460000044
And a reactive power reference value
Figure BDA0003134163460000045
And calculating to obtain:
Figure BDA0003134163460000046
as a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the control method of the modular multilevel converter comprises the following steps of establishing a mathematical model of currents of an MMC alternating-current port, an upper bridge arm and a lower bridge arm when an MIM (metal injection molding) in the multi-alternating-current port type modular multilevel converter only comprises a second single-phase converter, and converting the mathematical model into a d-q coordinate system which rotates synchronously with an alternating-current line 1 by Park to obtain the current of the modular multilevel converter:
Figure BDA0003134163460000047
wherein, Uod、Uoq、Iod、IoqRespectively the voltage u at the AC port of the MMCojAnd current iojD-q axis component of (1), Δ Vd、ΔVqRespectively MMC equivalent voltage Deltavj＝(unj-upj) D-q axis component of/2, upj、unjRespectively, an upper bridge arm equivalent voltage and a lower bridge arm equivalent voltage of MMC, L0、R0The bridge arm inductance L and the bridge arm resistance R are half of those of the MMC respectively, and j is a, b and c;
MMC alternating side current i by utilizing PI controllerojAnd performing closed-loop control, wherein a specific control equation is as follows:
Figure BDA0003134163460000048
wherein the superscripts denote reference values, k, of the respective componentspoAnd kioProportional and integral regulation coefficients, U, of a PI regulator in MMC current inner loop control, respectivelyod、UoqIs an MMC alternating-current port voltage disturbance suppression item for enhancing the anti-interference capability of a control loop, omega L0Iod、ωL0IoqIs a feedforward decoupling term; the MMC has an active current reference value
Figure BDA0003134163460000049
Reference value of reactive current
Figure BDA00031341634600000410
Reference value of reactive power
Figure BDA00031341634600000411
The calculation expression of (a) is as follows:
Figure BDA0003134163460000051
as a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: further comprising, when the second single-phase converter is not included in the MIM or two second single-phase converters are included in the multi-ac port type modular multi-level converter, the current i at the MMC ac portojThe sum of the currents of the AC lines is:
Figure BDA0003134163460000052
as a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: further comprising, when the MIM adopts the structure of scheme 2, the modulation wave of the upper bridge arm of the MMC
Figure BDA0003134163460000053
Modulated wave of lower bridge arm
Figure BDA0003134163460000054
The computational expressions included are as follows:
Figure BDA0003134163460000055
when the MIM adopts the structure of scheme 1, the modulation wave of the upper bridge arm of the MMC
Figure BDA0003134163460000056
Modulated wave of lower bridge arm
Figure BDA0003134163460000057
The computational expressions included are as follows:
Figure BDA0003134163460000058
when the MIM adopts the structure of scheme 3, the modulation wave of the upper bridge arm of the MMC
Figure BDA0003134163460000059
Modulated wave of lower bridge arm
Figure BDA00031341634600000510
The computational expressions included are as follows:
Figure BDA00031341634600000511
wherein,
Figure BDA00031341634600000512
fundamental frequency circulating current injected in an MMC bridge arm for controlling MIM energy balance and MMC upper and lower bridge arm energy balance.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the common direct current bus voltage balance control comprises that when the MIM adopts the topology of scheme 1, the control equation is as follows:
Figure BDA0003134163460000061
wherein, Vlinka、Vlinkb、VlinkcIs a three-phase common dc bus voltage,
Figure BDA0003134163460000062
three-phase reference voltage, k, for feed-forwardp1、ki1Respectively is a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller in the scheme;
the reference voltages are:
Figure BDA0003134163460000063
wherein,
Figure BDA0003134163460000064
the reference voltage is j-phase modulated for the first single-phase converter connected to the ac line 1,
Figure BDA0003134163460000065
j-phase modulation of a reference voltage, V, for a first single-phase converter connected to an AC line kcommon,dcA reference value of a DC component common to the first single-phase converter and the second single-phase converter, the reference value being greater than zero and less than the common DC bus voltage
Figure BDA0003134163460000066
When the MIM employs the topology of scheme 2, the control equation is as follows:
Figure BDA0003134163460000067
wherein k isp2、ki2Respectively a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller, and the feedforward term is 0;
the modulation reference voltage of each of the first single-phase converter and the second single-phase converter is as follows:
Figure BDA0003134163460000068
when the MIM employs the topology of scheme 3, the control equation is as follows:
Figure BDA0003134163460000069
wherein k isp3、ki3Respectively is a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller in the scheme;
the modulation reference voltage of each of the first single-phase converter and the second single-phase converter is as follows:
Figure BDA0003134163460000071
wherein,
Figure BDA0003134163460000072
the reference voltage is a three-phase reference voltage j alternating current reference voltage of a second single-phase converter connected with an upper bridge arm of the MMC.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the basic condition equation required to be satisfied by the distribution mode of the alternating-current equivalent voltage of the first single-phase converter and the second single-phase converter comprises that when the MIM adopts the topology of scheme 1, the equivalent alternating-current component of the output voltage of the first single-phase converter and the line current satisfy the following relation:
Figure BDA0003134163460000073
wherein,
Figure BDA0003134163460000074
to be connected with an AC line 1Outputs a vector representation of the ac component of the voltage,
Figure BDA0003134163460000075
outputting a vector representation of the AC component of the voltage for a first single-phase converter of said multi AC port type modular multilevel converter connected to an AC line k,
Figure BDA0003134163460000076
a vector expression of a series equivalent voltage AC component between the AC line 1 and the AC line k required for the purpose of performing the target power flow control for the AC line k,
Figure BDA0003134163460000077
expressed as the conjugate of the AC current vector on line k, VlinkVoltage magnitude between common DC buses in MIM for multi-AC port modular multilevel converter, IdcThe method comprises the steps that MMC current flows out of the direct current side of the multi-alternating current port type modular multi-level converter, and n is the number of alternating current lines which are interconnected with each other at the alternating current side of the multi-alternating current port type modular multi-level converter;
when the MIM adopts the topology of scheme 2, the line current of each first single-phase converter and each second single-phase converter meets the following basic conditions:
Figure BDA0003134163460000078
wherein,
Figure BDA0003134163460000079
is a vector expression of the equivalent voltage alternating current component of the second single-phase converter connected with the MMC,
Figure BDA00031341634600000710
is a conjugate expression of the alternating current vector flowing into the MMC alternating current port;
when the MIM adopts the topology of scheme 3, the line current of each first single-phase converter and each second single-phase converter and the injected fundamental frequency circulating current meet the following basic conditions:
Figure BDA0003134163460000081
wherein,
Figure BDA0003134163460000082
is a vector expression of the equivalent voltage alternating current component of the second single-phase current converter connected with the upper bridge arm and the lower bridge arm of the MMC,
Figure BDA0003134163460000083
for a conjugate expression of the sum of the ac line current vectors,
Figure BDA0003134163460000084
is a conjugate expression of the injected fundamental circulating current.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the first single-phase converter and the second single-phase converter have distribution mode of alternating-current equivalent voltage
Figure BDA0003134163460000085
The selection comprises the following steps that the distribution mode of the series equivalent voltage of the multi-end flexible interconnection module on the distribution network feeder line is as follows:
Figure BDA0003134163460000086
in the case of MIM employing scheme 1,
Figure BDA0003134163460000087
a feed-forward term for the output voltage of the single-phase converter connected in series with the line 1; the above-mentioned
Figure BDA0003134163460000088
Is selected to satisfy the maximum amplitude of the AC component of the output voltage of each of the first single-phase converter and the second single-phase converterMinimum large value: when the MIM adopts the topology of scheme 1, the
Figure BDA0003134163460000089
Is selected to satisfy
Figure BDA00031341634600000810
Taking the minimum value; when the MIM adopts the topology of scheme 2, the
Figure BDA00031341634600000811
Is selected to satisfy
Figure BDA00031341634600000812
Taking the minimum value; when the MIM adopts the topology of scheme 3, the
Figure BDA00031341634600000813
Is selected to satisfy
Figure BDA00031341634600000814
Taking the minimum value.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the overvoltage protection strategy of the voltage of the multi-alternating-current port type modular multi-level converter connected on the feeder line in series comprises that a protection device is connected in parallel between alternating-current output ports of a first single-phase converter in the multi-terminal flexible interconnection module; the protection device is formed by connecting a metal oxide voltage limiter and a thyristor bypass switch in parallel, the metal oxide voltage limiter limits the voltage at a protection level, and the thyristor bypass switch bypasses an alternating current output port of the first single-phase converter; the thyristor bypass switch is formed by connecting an anti-parallel thyristor, a resistance-capacitance loop and a static resistor in parallel and then connecting the thyristor bypass switch with a saturable reactor in series.
As a preferable scheme of the control method of the multi-ac port modular multilevel converter according to the present invention, wherein: the starting strategy of the multi-alternating current port type modularized multi-level converter comprises the following steps: in the uncontrolled charging stage, the alternating current circuit 1 is connected with a current-limiting resistor in series and is connected to the grid, all switches are locked, and the current of the alternating current grid charges a capacitor in the multi-alternating current port type modular multilevel converter through a freewheeling diode of each switch; and a second stage: in the controlled charging stage, after the uncontrolled charging in the first stage is finished, the voltage of each capacitor does not reach a reference value, the number of the charged capacitors in a loop is constant in a switch alternate switching mode, and the voltage of the capacitor in the multi-alternating-current port type modular multilevel converter is further improved; and a third stage: a ramp boosting stage, after the charging in the second stage is finished, putting a voltage control loop and giving a reference voltage adopting ramp change, and charging the voltage of each capacitor to a reference value; a fourth stage: and in the input stage of the alternating current circuit, after charging is completed, the other alternating current circuits are matched with respective circuit current control rings and the reference given output of the first single-phase converter connected with the circuit current control rings to realize soft input.
The invention has the beneficial effects that: according to the invention, a multi-port flexible interconnection module (MIM) is innovatively introduced on the basis of a modular multilevel converter, a plurality of AC line feed-in ports are provided, and interconnection of a plurality of AC lines and a DC power grid in a station of the same converter station is realized; the active control of the power flow of the alternating current circuit can be realized by adjusting the amplitude and the phase of the alternating current component of the output voltage of the first single-phase converter connected with the alternating current circuit; compared with the existing common networking structure of the AC/DC converter station, the networking structure of the AC/DC converter station adopts a transformerless structure, adopts a mode of simultaneously feeding a plurality of AC lines and an AC/DC power grid interconnection mode, and has great advantages in the aspects of power density, converter station size, construction cost, power supply reliability, power supply system operation efficiency and the like; the flexible interconnection of the multiple alternating current lines is realized by utilizing the multi-terminal flexible interconnection module, the flexible interconnection has the characteristic of modularization, and the port expansion of the alternating current lines can be economically, efficiently and conveniently realized by increasing the number of the first single-phase converters in the interconnection module.
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In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the description of the embodiments will be briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive exercise. Wherein:
fig. 1 is a system schematic diagram of four typical networking structures of an ac/dc converter station of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 2 is a schematic diagram illustrating an exemplary topology of a voltage source type converter and a voltage source type single-phase converter of a multi-ac-port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 3 is a schematic diagram illustrating exemplary topologies of sub-modules of a modular multilevel converter according to an embodiment of the present invention, and a method for controlling the same;
fig. 4 is a system wiring diagram of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention, wherein the topology does not include a second single-phase converter, and the interconnected multi-ac lines thereof;
fig. 5 is a system wiring diagram of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention, wherein the system wiring diagram of the multi-ac port modular multilevel converter comprises a single second single-phase converter and interconnected multi-ac lines thereof;
fig. 6 is a system wiring diagram of a topology including two second single-phase converters and their interconnected multi-ac lines of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 7 is a schematic diagram of a flexible interconnection system of a multi-line multi-voltage-level ac/dc power grid using a single multi-ac-port modular multi-level converter as a core device according to a multi-ac-port modular multi-level converter and a control method thereof provided by an embodiment of the present invention;
fig. 8 is a schematic diagram of a flexible interconnection system of a multi-line multi-voltage-level ac/dc power grid using a plurality of multi-ac port type modular multi-level converters as core devices according to a multi-ac port modular multi-level converter and a control method thereof provided in an embodiment of the present invention;
fig. 9 is a wiring diagram of an overvoltage protection mode of a single-phase converter and a protection device of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 10 is a schematic diagram of a converter station topology and system wiring in which the multi-ac port modular multilevel converter and the control method thereof according to an embodiment of the present invention are configured as shown in fig. 5, and sub-modules of the first single-phase converter, the second single-phase converter and the modular multilevel converter of the multi-port flexible interconnection apparatus all adopt a two-level half-bridge converter topology to realize interconnection of two ac lines;
fig. 11 is a control block diagram of a converter station in which a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention are configured as shown in fig. 5, and sub-modules of a first single-phase converter, a second single-phase converter and the modular multilevel converter of a multi-port flexible interconnection apparatus all adopt a two-level half-bridge converter topology to implement interconnection of two ac lines;
fig. 12 is a diagram of waveforms of dc line active power, ac line currents, dc side currents, and intra-device sub-module capacitor voltages under simulation of a first operating mode of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 13 is a diagram of waveforms of dc line active power, ac line currents, dc side currents, and intra-device sub-module capacitor voltages under simulation of a second operating mode of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 14 is a diagram of waveforms of active power of a dc line, power flow of each ac line, line current, dc-side current, and capacitor voltage of sub-modules in the device under simulation of a third operating condition of a multi-ac-port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 15 is a diagram of waveforms of dc line active power, ac line power flow, line current, dc side current, and intra-device sub-module capacitor voltage under simulation of a fourth operating mode of a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention;
fig. 16 is a schematic diagram of a converter station topology and system wiring, in which a multi-ac-port modular multilevel converter and a control method thereof according to an embodiment of the present invention are configured as shown in fig. 5, and sub-modules of a first single-phase converter, a second single-phase converter and the modular multilevel converter of a multi-port flexible interconnection apparatus all adopt a two-level half-bridge converter topology to implement interconnection of three ac lines;
fig. 17 is a control block diagram of a converter station in which a multi-ac port modular multilevel converter and a control method thereof according to an embodiment of the present invention adopt the structure shown in fig. 5, and sub-modules of a first single-phase converter, a second single-phase converter and the modular multilevel converter of a multi-port flexible interconnection apparatus all adopt a two-level half-bridge converter topology to implement interconnection of three ac lines;
fig. 18 is a diagram of dc line active power, ac line power flow, line current, dc side current and intra-device sub-module capacitor voltage waveforms in a simulation of a multi-ac port modular multilevel converter and a method for controlling the same according to an embodiment of the present invention;
fig. 19 is a diagram of dc line active power, ac line power flow, line current, dc side current and intra-device sub-module capacitor voltage waveforms in another simulation of a multi-ac port modular multilevel converter and a method for controlling the same according to an embodiment of the present invention.
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, specific embodiments accompanied with figures are described in detail below, and it is apparent that the described embodiments are a part of the embodiments of the present invention, not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without making creative efforts based on the embodiments of the present invention, shall fall within the protection scope of the present invention.
In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways than those specifically described and will be readily apparent to those of ordinary skill in the art without departing from the spirit of the present invention, and therefore the present invention is not limited to the specific embodiments disclosed below.
Furthermore, reference herein to "one embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one implementation of the invention. The appearances of the phrase "in one embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments.
The present invention will be described in detail with reference to the drawings, wherein the cross-sectional views illustrating the structure of the device are not enlarged partially in general scale for convenience of illustration, and the drawings are only exemplary and should not be construed as limiting the scope of the present invention. In addition, the three-dimensional dimensions of length, width and depth should be included in the actual fabrication.
Meanwhile, in the description of the present invention, it should be noted that the terms "upper, lower, inner and outer" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation and operate, and thus, cannot be construed as limiting the present invention. Furthermore, the terms first, second, or third are used for descriptive purposes only and are not to be construed as indicating or implying relative importance.
The terms "mounted, connected and connected" in the present invention are to be understood broadly, unless otherwise explicitly specified or limited, for example: can be fixedly connected, detachably connected or integrally connected; they may be mechanically, electrically, or directly connected, or indirectly connected through intervening media, or may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
Example 1
The networking structure of the ac/dc converter station may affect various aspects such as system cost, power supply reliability, protection configuration, and control flexibility. According to the difference of the connection modes of the ac-dc converter station, the networking structure thereof can be divided into 4 types, as shown in fig. 1(a) - (d), which are: the converter station comprises a single alternating current line, a single converter station, a single direct current bus, multiple alternating current lines, multiple converter stations, multiple direct current buses and a hybrid type. Hereinafter, the 4 structures are respectively referred to as schemes a-d, and the networking structure of the existing power supply network can be regarded as the schemes a-c; in the scheme a, the energy of the direct current power grid is supplied by a single alternating current bus, so that the power supply reliability is general, and the power supply range is small; according to the scheme b, a plurality of alternating current lines are introduced on the basis of the scheme a to form a multi-terminal radiation type power supply network, the alternating current lines are mutually standby, the power supply reliability is improved, the standby line cost is increased, and the problems of an electromagnetic ring network and reactive circulation exist at the same time; each alternating current line in the scheme c is connected to a direct current bus through a converter station, each direct current bus can operate in a segmented mode, flexible interconnection operation can be achieved, and the scheme has the advantages of being high in flexibility, high in power supply reliability and high in cost; and in the scheme d, a multi-end alternating current circuit is directly fed into the converter station, and the flexible adjustment of the circuit tide and the power coordination among the circuits are realized by utilizing a coordination control means, so that the reactive circulation problem of the scheme b is effectively solved, and the cost and the power density are far better than those of the scheme c while the flexible interconnection requirement of the scheme c is met.
Therefore, the invention provides a multi-alternating current port type modular multilevel converter suitable for a medium-high voltage alternating current and direct current hybrid power grid and a control method thereof on the basis of the scheme d, and the invention meets the application requirements of low cost, high power density and the like on the basis of realizing the function of a multi-alternating current circuit.
Referring to fig. 1 to 9, in an embodiment of the present invention, a multi-ac port modular multilevel converter and a control method thereof are provided, including:
a modular multilevel converter; and
a multi-port flexible interconnect module in series with the modular multilevel converter.
Specifically, the invention provides a multi-port modular multilevel converter with active power flow control capability, which is suitable for a medium-high voltage alternating current and direct current hybrid power grid, and realizes the conversion of a multi-terminal alternating current circuit and a medium-high voltage direct current power grid in the same converter station; the Multi-ac port type Modular Multilevel Converter includes a Modular Multilevel Converter (MMC) and a Multi-port interconnection module (MIM) connected in series with the Modular Multilevel Converter (MMC).
The MMC in the multi-AC port type modular multilevel converter is a medium-high voltage level voltage source type converter and has an active power bidirectional flowing function, and active power can flow from an AC side to a DC side and also can flow from the DC side to the AC side. The MIM in the multi-AC port type modular multilevel converter comprises a plurality of first single-phase converters connected in parallel on a common connection bus, and an AC output port of each single-phase converter is connected with a corresponding AC line, wherein the common connection bus is a medium-low voltage DC bus, and a common connection capacitor connected with the common connection bus provides voltage support for the common connection bus; by changing the amplitude and the phase of the alternating current component in the output voltage of the first single-phase converter, the flexible adjustment of the alternating current line power flow connected with the first single-phase converter can be actively realized. The ac component of the output voltage of the first single-phase converter connected in series with the ac line is hereinafter referred to as the series equivalent voltage.
Further, as shown in fig. 3, the MMC sub-module topology may be a half-bridge sub-module topology, a full-bridge sub-module topology, a clamped dual sub-module topology, or a topology that adopts other feasible structures and a hybrid of multiple structures.
Furthermore, the MIM can be divided into three schemes according to whether the second single-phase converter is included and the connection modes of the included second single-phase converter and the MMC upper and lower bridge arms are different, as shown in fig. 4, 5 and 6; the three schemes can realize flexible interconnection between a plurality of alternating current lines and a direct current power grid; specifically, in the scheme 1, the MIM does not include the second single-phase converter, the ac output ports of the upper and lower bridge arms of the MMC are respectively connected to the positive and negative electrodes of the common dc bus of the MIM, and the balance of the MIM energy is maintained by adjusting the output voltage of the first single-phase converter connected to the reference line, thereby ensuring the stability of the voltage of the common dc bus; in the scheme 2, the MIM includes a second single-phase converter which is connected in parallel with the first single-phase converter at two ends of the common direct current bus, and the alternating current port of the MMC is connected with the alternating current output port of the second single-phase converter, so that the balance between MIM absorption and active power generation can be realized by adjusting the amplitude and phase of the alternating current output voltage of the second single-phase converter except for the method in the scheme 1; in the scheme 3, the MIM includes a first single-phase converter and two second single-phase converters, the number of which is matched with that of the ac lines, the first single-phase converter and the two second single-phase converters are connected in parallel at two ends of a common dc bus, and ac output ports of the two second single-phase converters are respectively connected with ac output ports of an upper bridge arm and a lower bridge arm of the MMC.
The first single-phase converter and the second single-phase converter are both voltage source type single-phase converters; the topology of the first single-phase converter or the second single-phase converter in the MIM may be a two-level half-bridge converter, a three-level half-bridge converter, or another single-phase bridge converter capable of realizing bidirectional power flow.
In addition, the invention provides a control method applied to a multi-alternating current port modular multilevel converter, which comprises the following steps: alternating current line power flow control, modular multilevel converter control and common direct current bus voltage balance control.
In particular, multiple AC port type modularityThe multilevel converter realizes flexible interconnection of a plurality of alternating current lines and a direct current power grid through cooperative control of the multi-end flexible interconnection module and the MMC, and can flexibly adjust the power flow distribution on the plurality of lines to meet the power consumption requirement of a direct current side load; when the multi-section flexible interconnection module is interconnected with n alternating current lines, the power flow P on each alternating current line needs to be controlled according to the demand of power flow control of the system1～PnAnd Q1～QnAnd DC side load power PLThe control is carried out, but considering factors such as line loss, device loss and the like, the active power of one AC line is automatically adjusted through the energy balance of the system, so that only the reactive power on the line needs to be controlled; hereinafter, the ac line is referred to as an ac line 1, and the other ac lines are referred to as ac lines k (k ═ 2.., n).
In the control of the multi-port modular multilevel converter, a three-phase alternating current component locked by a phase-locked loop is the three-phase node voltage of an alternating current line 1 controlled by constant reactive power, and the voltage current under a three-phase alternating current a-b-c coordinate system is converted into a d-q coordinate system through Park conversion to perform active and reactive component decoupling control through the phase of the real-time output power grid voltage.
More specifically, the three control methods of the ac line power flow control, the MMC control, and the common connection bus voltage balance control are described as follows:
(1) the control objective of the ac line power flow control is that the reactive power of the ac line 1 reaches a reference value
Figure BDA0003134163460000151
The active power of the AC line k reaches the reference value
Figure BDA0003134163460000152
And the reactive power of the AC line k reaches the reference value
Figure BDA0003134163460000153
For line power flow control, the voltage v of the 1-node of the line is written by taking the AC line 1 as a reference1jNode voltage v to line kkjThe following equation can be obtained by converting the dynamic equation into a d-q coordinate system:
Figure BDA0003134163460000154
wherein, V1d、V1q、Vkd、Vkq、I1d、I1q、Ikd、IkqD-q axis components, L, of line 1 and line k node voltage currents, respectively1、R1、Lk、RkThe inductance and the equivalent resistance on the line 1 and the line k respectively, omega represents the angular frequency of the power grid, delta Uc1kd、ΔUc1kdIs an equivalent voltage Deltauc1kj＝uc1j-uckjD-q axis component of (u)c1jIs the AC component of the output voltage of a first single-phase converter connected to an AC line 1ckjThe ac component in the output voltage of the first single-phase converter connected to the ac line k is (j ═ a, b, c).
Wherein, the line power flow control is carried out under a d-q coordinate system, and the output is delta Uc1kdAnd Δ Uc1kdAfter Park inverse transformation, the three-phase equivalent voltage difference delta u of the first converter between the line 1 and the line k can be obtainedc1kj. Due to the presence of L in the above formula1dI1d/dt+I1dR1、L1dI1q/dt+I1qR1、LkdIkd/dt+IkdRk、LkdIkq/dt+IkqRkAnd if the differential link is incorporated into a feedforward disturbance elimination link of the power flow control loop, the performance of the control loop is reduced to a certain degree. Therefore, when designing a control loop, the derivative term is ignored, and a PI controller is used to perform closed-loop control on the current on the line k, and a specific control equation is as follows:
Figure BDA0003134163460000155
wherein the superscripts denote reference values, k, of the respective componentspkAnd kikProportional and integral coefficients, V, of a power flow control loop PI regulator of line k, respectively1d、V1q、Vkd、VkqThe anti-interference capability of the power flow control loop on line node voltage is improved as a feedforward term, omega L1I1d、ωL1I1q、ωLkIkd、ωLkIkqThe decoupling method is a feedforward decoupling item and can realize the decoupling of d-axis active power control and q-axis reactive power control.
The d-axis component reference value of the line current of the alternating current line power flow control loop is determined by the following relation between the line target power flow and the line node voltage and current
Figure BDA0003134163460000156
And q-axis component reference value
Figure BDA0003134163460000157
According to the active power reference value of the AC line k
Figure BDA0003134163460000158
And a reactive power reference value
Figure BDA0003134163460000159
And calculating to obtain:
Figure BDA0003134163460000161
(2) the MMC in the multi-AC port type modular multilevel converter has the control target that the constant power control of the DC side of the MMC reaches a reference value
Figure BDA0003134163460000162
And constant reactive power control of the AC line 1 to a reference value
Figure BDA0003134163460000163
According to different MMC control links, the MMC control can be controlled by outer ring active power, outer ring reactive power and inner ringThe MMC control also comprises fundamental frequency circulating current injection control when the topological structure in the scheme 3 is adopted; the capacitance voltage balance control and double-frequency circulating current suppression functions in the three schemes of the multi-AC port type modular multilevel converter are consistent with those of the conventional MMC.
If the MIM of the multi-ac port type modular multi-level converter includes only one second single-phase converter, the topology of scheme 2 is considered; aiming at MMC control, a mathematical model of the current of an MMC alternating current port and the current of an upper bridge arm and a lower bridge arm is established, and Park is carried out to convert the mathematical model into a d-q coordinate system which rotates synchronously with an alternating current line 1, so that the mathematical model can be obtained:
Figure BDA0003134163460000164
wherein, Uod、Uoq、Iod、IoqRespectively the voltage u at the AC port of the MMCojAnd current iojD-q axis component of (1), Δ Vd、ΔVqRespectively MMC equivalent voltage Deltavj＝(unj-upj) D-q axis component of/2, upj、unjRespectively an upper bridge arm equivalent voltage and a lower bridge arm equivalent voltage of the MMC; l is0、R0Half of the MMC bridge arm inductance L and bridge arm resistance R, respectively, (j ═ a, b, c).
MMC current inner ring control in the multi-AC port type modular multilevel converter is carried out under a d-q coordinate system, and the output of the MMC current inner ring control is delta VdAnd Δ VqAfter Park inverse transformation, MMC equivalent voltage delta v can be obtainedj(ii) a Due to the presence of L in the above formula0dIod/dt+R0IodAnd L0dIoq/dt+R0IoqA differentiation step, which is to ensure the performance of the control loop and ignore the differentiation step; MMC alternating side current i by utilizing PI controllerojAnd performing closed-loop control, wherein a specific control equation is as follows:
Figure BDA0003134163460000165
wherein the superscripts denote reference values, k, of the respective componentspoAnd kioProportional and integral regulation coefficients, U, of a PI regulator in MMC current inner loop control, respectivelyod、UoqIs an MMC alternating-current port voltage disturbance suppression item for enhancing the anti-interference capability of a control loop, omega L0Iod、ωL0IoqThe decoupling method is a feedforward decoupling item and can realize the decoupling of d-axis active power control and q-axis reactive power control.
If the MIM of the multi-ac port type modular multilevel converter does not include the second single-phase converter or includes two second single-phase converters, i.e., the above-mentioned schemes 1 and 3, the MMC ac port voltage u in the above-mentioned MMC control is performedojEquivalent is the equivalent alternating voltage on the MIM public connection bus, and the current i at the alternating current port of the MMCojIs the sum of the currents of the AC lines
Figure BDA0003134163460000171
Since the PLL is based on the node voltage on the AC line 1, the MMC has an active current reference value
Figure BDA0003134163460000172
Loaded by a direct current side
Figure BDA0003134163460000173
And a reactive current reference value
Figure BDA0003134163460000174
Calculate given, and
Figure BDA0003134163460000175
then from the q-axis current reference on the AC line 2-n
Figure BDA0003134163460000176
And the reactive power reference value of the AC line 1
Figure BDA0003134163460000177
Collectively, the computational expression is as follows:
Figure BDA0003134163460000178
if the MIM in the multi-AC port type modular multi-level converter adopts the structure of the scheme 2, the MMC modulation in the scheme is consistent with the conventional MMC modulation, and the modulation wave of the upper bridge arm of the MMC
Figure BDA0003134163460000179
Modulated wave of lower bridge arm
Figure BDA00031341634600001710
All comprise an equivalent voltage deltav at the alternating current port generated by MMC inner ring current controljHalf U of the voltage of the MMC DC sidedc/2 and double frequency AC voltage u for double frequency loop current suppression on bridge arm of MMCdiffjThe specific calculation expression is as follows:
Figure BDA00031341634600001711
if the MIM in the multi-AC-port modular multi-level converter adopts the structure of scheme 1, in the scheme, because the upper bridge arm and the lower bridge arm of the MMC are respectively connected with the positive and negative DC buses of the MIM, the AC output ports of the two bridge arms have a common DC bus voltage VlinkThe direct current bias of (2) is uniformly distributed into the modulation of an upper bridge arm and a lower bridge arm of the MMC, namely:
Figure BDA00031341634600001712
if the MIM in the multi-AC port type modular multi-level converter adopts the structure of scheme 3, two second single-phase converters exist in the scheme, and if the AC/DC components of the output voltages of the two second single-phase converters are completely consistent, the scheme is adoptedScheme 2 can be converted; if the AC components of the output voltages of the two second single-phase converters are 0, and one of the DC components is 0, the other DC component is VlinkThen the scheme may be changed to scheme 1; in addition, the alternating current-direct current components in the output voltages of the two single-phase converters in the scheme 3 can be freely changed within a certain range according to the requirement of energy balance; considering that the degree of freedom of control in the scheme 3 is high, the direct current components of the two single-phase converters are controlled to be consistent, so that the circulating current on the bridge arm of the MMC has an effect of adjusting the energy balance of the MIM, the alternating current components of the output voltages of the two single-phase converters are inconsistent, and the alternating current component of the output voltage of the second single-phase converter connected with the bridge arm on the MMC is ucsm1jAnd the alternating current component of the output voltage of the second single-phase current converter connected with the MMC lower bridge arm is ucsm2j(ii) a In order to balance the energy of the upper and lower bridge arms of the MMC, the energy is incorporated into a bridge arm modulation reference wave of the MMC, and a calculation expression is as follows:
Figure BDA0003134163460000181
wherein,
Figure BDA0003134163460000182
fundamental frequency circulating current injected in an MMC bridge arm for controlling MIM energy balance and MMC upper and lower bridge arm energy balance; due to the output voltage u of the two second single-phase converters in the MIMcsm1jAnd ucsm2jThe component can influence the balance of the energy of the upper and lower bridge arms of the original MMC, so that the injected fundamental frequency circulating current can influence the energy absorbed by the MIM and can play a role in transferring the energy to the upper and lower bridge arms of the MMC; in conclusion, the fundamental frequency circulating current injection control strategy and the MIM balance control strategy corresponding to the third part cooperate to balance the energy of the upper and lower bridge arms of the MIM and the MMC, so that the stability of the system is maintained.
If the MIM in the multi-AC port type modular multi-level converter adopts the structure of scheme 3, a certain fundamental frequency circulating current needs to be injected to ensure the energy balance of the MIM and MMC devices. Due to the two second in MIMOutput voltage u of single-phase convertercsm1jAnd ucsm2jAC port equivalent voltage Deltav relative to MMCjThe injected circulating current is expected to expand the adjusting range of the multi-port type modular multilevel converter for the alternating current line power flow as much as possible, so that the phase of the circulating current lags behind the MMC equivalent voltage pi/2, the effect of the circulating current on the original upper and lower bridge arm energy relocation of the MMC is enabled to be as small as possible, and the voltage generated by the circulating current on the bridge arm inductor and the MMC equivalent voltage delta v at the moment are smaller than the MMC equivalent voltage delta vjIn phase; to MMC equivalent voltage DeltavjCarrying out Park conversion to convert the voltage into a d-q coordinate system synchronously rotating with the line 1, and obtaining the MMC equivalent voltage delta v by using a d-q axis component after the d-q conversionjThe phase of (1), the MMC equivalent voltage output by the MMC inner ring current control is utilized in the control
Figure BDA0003134163460000198
And calculating a reference value, wherein a specific calculation expression is as follows:
Figure BDA0003134163460000191
wherein,
Figure BDA0003134163460000192
three-phase MMC equivalent voltage reference value respectively for MMC inner ring current control output
Figure BDA0003134163460000193
Converting to reference values for d-axis and q-axis components; because the injected fundamental frequency circulation lags behind the MMC equivalent voltage reference value pi/2, the circulation component is at the MMC equivalent voltage reference value
Figure BDA0003134163460000194
Only a q-axis component exists in the oriented d-q synchronous rotating coordinate system, and the energy transfer of the oriented d-q synchronous rotating coordinate system to the upper bridge arm and the lower bridge arm is small.
In summary, a solution is provided for MMC control and modulation under three schemes in the multi-ac port type modular multilevel converter, and other feasible control and modulation schemes may be adopted; for example, in case of scheme 3, the second single-phase converter connected to the MMC may adopt a double-frequency modulation mode, and a double-frequency circulating current is injected into a corresponding arm of the MMC to balance the energy of the MIM, and a fundamental circulating current is injected into the arm of the MMC to balance the energy of the upper and lower arms.
(3) The control target of the common direct current bus voltage balance control loop is that the common direct current bus voltage is stabilized at a reference value
Figure BDA0003134163460000199
And the control of the common direct current bus voltage balance control loop is carried out under an a-b-c coordinate system, the output of the common direct current bus voltage balance control loop is the reference voltage of the first single-phase converter or the second single-phase converter for MIM energy balance, and the common direct current bus voltage of the a-b-c three phases is controlled by using a proportional-integral controller.
If the topology of scheme 1 is adopted by the MIM in the multi-AC port type modular multi-level converter, the scheme does not comprise a second single-phase converter, and the output of the common DC bus voltage balance control loop is the reference voltage of a first single-phase converter connected with the line 1
Figure BDA0003134163460000195
In order to fully play the role of the single-phase converter on MIM balance control, j alternating current voltage reference value of the single-phase converter
Figure BDA0003134163460000196
J-phase current i with line 11jIn the same direction, the control equation is as follows, (j ═ a, b, c):
Figure BDA0003134163460000197
wherein, Vlinka、Vlinkb、VlinkcFor three-phase common DC bus voltage, adopted under three schemes
Figure BDA0003134163460000201
Figure BDA0003134163460000202
The three-phase reference voltage is feedforward, and the given k can be calculated according to any one of the equivalent voltage distribution modes of the first single-phase converterp1、ki1The gain coefficient of the proportional-integral controller in the scheme is the gain coefficient of the proportional link and the gain coefficient of the integral link.
If the MIM in the multi-AC-port type modular multilevel converter adopts the topology of the scheme 1, the j-phase reference voltage is obtained at the output of the power flow control loop of the AC line k
Figure BDA0003134163460000203
And a common DC bus balance control loop outputting a j AC reference voltage of a first single-phase converter connected to the AC line 1
Figure BDA0003134163460000204
Then, the reference voltage of the first single-phase converter connected to each ac line is:
Figure BDA0003134163460000205
wherein,
Figure BDA0003134163460000206
the reference voltage is j-phase modulated for the first single-phase converter connected to the ac line 1,
Figure BDA0003134163460000207
j-phase modulation of a reference voltage, V, for a first single-phase converter connected to an AC line kcommon,dcA reference value of a DC component common to the first single-phase converter and the second single-phase converter, the reference value being greater than zero and less than the common DC bus voltage
Figure BDA0003134163460000208
MIM (metal-insulator-metal) adoption scheme in multi-AC (alternating current) port type modularized multi-level converter2, the scheme comprises a second single-phase converter, and the output of the common direct current bus voltage balance control loop is j-phase reference voltage of the second single-phase converter connected with the MMC alternating current port
Figure BDA0003134163460000209
In order to fully exert the energy regulation effect of the second single-phase converter on the MIM, the j alternating current voltage reference value of the second single-phase converter
Figure BDA00031341634600002010
J phase current i of MMC alternating current portojIn the reverse direction, the control equation is as follows, (j ═ a, b, c):
Figure BDA00031341634600002011
wherein k isp2、ki2The proportional link gain coefficient and the integral link gain coefficient of the proportional-integral controller in the scheme are different from the common direct current bus voltage balance control in the scheme 1, and the feedforward term in the scheme 2 is 0.
If the MIM in the multi-AC-port type modular multilevel converter adopts the topology of the scheme 2, the j-phase reference voltage is obtained by controlling the power flow control loop of the AC line k
Figure BDA00031341634600002012
And the common direct current bus balance control loop outputs the j alternating current reference voltage of the second single-phase current converter connected with the MMC alternating current port
Figure BDA00031341634600002013
And then, the modulation reference voltage of each first single-phase converter and each second single-phase converter is as follows:
Figure BDA0003134163460000211
if the MIM in the multi-ac port type modular multilevel converter adopts the topology of scheme 3, which includes two second single-phase converters, the effect of the different output voltages of the second single-phase converters on the MMC control and modulation has been described in the above section, and in addition, the common dc bus voltage balance control in the MIM is changed accordingly.
If the MIM in the multi-AC port type modular multi-level converter adopts the topology of scheme 3, when the tide of an AC line is in a certain range, the MIM device can control the output voltages of two second single-phase converters connected with an upper bridge arm and a lower bridge arm of an MMC to be consistent when the energy balance can be realized through the energy interaction between the first single-phase converter and the second single-phase converter and the voltage of each AC line, and the phase position of each phase of the MIM device is the phase position of the sum of the current of each AC line
Figure BDA0003134163460000212
The consistency is achieved; when the power flow of the alternating current line exceeds a certain range, the MIM device cannot realize energy balance through energy interaction between the first single-phase current converter and the second single-phase current converter and the voltage of each alternating current line, the MIM energy needs to be balanced on an MMC bridge arm by adopting a fundamental frequency circulating current injection mode, and the output of the common direct current bus voltage balance control is the alternating current reference voltage of the second single-phase current converter connected with the lower bridge arm of the MMC
Figure BDA0003134163460000213
In order to fully play the energy regulation effect of the injected fundamental frequency circulating current on the MIM, the j alternating current voltage reference value of the second single-phase converter is controlled
Figure BDA0003134163460000214
J-phase current i circulating with injected fundamental frequencycirjIn the same direction, the control equation is as follows, (j ═ a, b, c):
Figure BDA0003134163460000215
wherein k isp3、ki3The gain coefficient of the proportional-integral controller in the scheme is the gain coefficient of the proportional link and the gain coefficient of the integral link.
If the MIM in the multi-AC-port type modular multilevel converter adopts the topology of the scheme 3, the j-phase reference voltage is obtained by controlling the power flow control loop of the AC line k
Figure BDA0003134163460000216
And the common direct current bus balance control loop outputs the j alternating current reference voltage of the second single-phase current converter connected with the MMC alternating current port
Figure BDA0003134163460000217
And then, the modulation reference voltage of each first single-phase converter and each second single-phase converter is as follows:
Figure BDA0003134163460000218
wherein,
Figure BDA0003134163460000221
the three-phase reference voltage j of the second single-phase converter connected with the upper bridge arm of the MMC can be given according to the open-loop calculation mode of the invention.
The above-mentioned common dc bus balance control schemes for the MIM three schemes in the multi-ac port type modular multilevel converter provide a solution, respectively, and certainly other feasible balance control schemes can also be adopted.
According to the basic idea of the control and modulation strategy of the three schemes, the invention provides a plurality of distribution modes of the alternating current equivalent voltage of the first single-phase converter and the second single-phase converter of the multi-alternating-current port type modular multi-level converter under the three schemes; according to the explanation of the control and modulation idea of the third scheme in the second aspect, the dc components in the reference voltages of the first single-phase converter and the second single-phase converter are identical and are both Vcommon,dc。
If the MIM in the multi-ac port type modular multilevel converter adopts the topology of scheme 1, that is, the interconnection module does not include the second single-phase converter, each first single-phase converter is respectively in energy interaction with the ac line connected to it, in order to balance the energy of the MIM, the equivalent ac component of the output voltage of the first single-phase converter and the line current must satisfy the following relationship:
Figure BDA0003134163460000222
wherein, the node voltage of the AC line 1 is the reference voltage of the whole control system, the line 1 is a constant reactive power AC line,
Figure BDA0003134163460000223
is a vector representation of the ac component of the output voltage of the first single-phase converter connected to the ac line 1,
Figure BDA0003134163460000224
a vector representation of the ac component of the output voltage of a first single-phase converter connected to an ac line k for a modular multilevel converter of the multiple ac port type,
Figure BDA0003134163460000225
a vector expression of a series equivalent voltage AC component between the AC line 1 and the AC line k required for the purpose of performing the target power flow control for the AC line k,
Figure BDA0003134163460000226
expressed as the conjugate of the AC current vector on line k, VlinkVoltage magnitude between common DC buses in MIM for multi-AC port modular multilevel converter, IdcThe direct current side of the multi-alternating current port type modular multi-level converter flows the current of the MMC, and n is the number of alternating current lines which are interconnected with each other at the alternating current side of the multi-alternating current port type modular multi-level converter.
If the MIM of the multi-ac port type modular multilevel converter adopts the topology of scheme 1, the multiple distribution modes of the ac equivalent voltage of the first single-phase converter in the MIM are any one set of solutions satisfying the above equation set
Figure BDA0003134163460000227
Further, the optimal distribution method of the equivalent voltage alternating current component of each first single-phase converter comprises the following steps
Figure BDA0003134163460000228
Is selected such that the amplitude of the alternating current component of the output voltage of each first single-phase converter is minimal, i.e.
Figure BDA0003134163460000231
Thereby obtaining the maximum ac line power flow regulation range.
If the MIM in the multi-ac port type modular multilevel converter adopts the topology of scheme 2, i.e. the interconnection module includes a second single-phase converter. The line current of each first single-phase converter and each second single-phase converter must satisfy the following basic conditions to realize the stable control of the line power flow:
Figure BDA0003134163460000232
wherein,
Figure BDA0003134163460000233
is a vector expression of the equivalent voltage alternating current component of the second single-phase converter connected with the MMC,
Figure BDA0003134163460000234
is a conjugate expression of the alternating current vector flowing into the MMC alternating current port.
If the MIM of the multi-ac port type modular multilevel converter adopts the topology of scheme 2, the plurality of distribution manners of the equivalent voltage ac component of the first single-phase converter in the MIM are any one set of solutions satisfying the above equation set
Figure BDA0003134163460000235
Furthermore, a component of the equivalent voltage AC component of the first single-phase converter connected to the line 1Is prepared by selecting
Figure BDA0003134163460000236
The reference value of the AC output voltage of the other first single-phase current converter is obtained by the formula
Figure BDA0003134163460000237
Respectively obtained by calculation, and the method is characterized by simple calculation. The optimal distribution method of the equivalent voltage alternating current components of each first single-phase converter comprises
Figure BDA0003134163460000238
Is selected such that the amplitude of the ac component of the output voltage of each of the first and second single-phase converters is minimal, i.e.
Figure BDA0003134163460000239
And the minimum, thereby obtaining the maximum regulating range of the AC line power flow.
If the MIM in the multi-ac port type modular multilevel converter adopts the topology of scheme 3, that is, the interconnection module includes two second single-phase converters, the line current of each first single-phase converter and the second single-phase converter and the injected fundamental frequency circulating current must satisfy the following basic conditions to realize the stable control of the line power flow:
Figure BDA00031341634600002310
wherein,
Figure BDA00031341634600002311
is a vector expression of the equivalent voltage alternating current component of the second single-phase current converter connected with the upper bridge arm and the lower bridge arm of the MMC,
Figure BDA00031341634600002312
for a conjugate expression of the sum of the ac line current vectors,
Figure BDA00031341634600002313
for injection ofConjugate expression of fundamental circulation.
If the MIM of the multi-ac port type modular multilevel converter adopts the topology of scheme 3, the plurality of distribution manners of the equivalent voltage ac component of the first single-phase converter in the MIM are any one set of solutions satisfying the above equation set
Figure BDA0003134163460000241
Furthermore, one distribution mode of the equivalent voltage alternating current component of each first single-phase current converter is to select
Figure BDA0003134163460000242
Is characterized by its simplicity.
Furthermore, the selection of the equivalent voltage alternating current component of each first single-phase converter and each second single-phase converter is closely related to the selection of the injected circulating current, and in order to fully ensure the adjusting capacity of the whole device for alternating current circuit power flow and the energy balance of the upper bridge arm and the lower bridge arm of the MMC, the optimal distribution method of the equivalent voltage is that
Figure BDA0003134163460000244
Is selected such that the maximum value of the amplitude of the alternating current component of the output voltage of each of the first single-phase converter and the second single-phase converter is the minimum, i.e.
Figure BDA0003134163460000243
And the injected circulation component is minimized on the basis of the minimum value.
In summary, three schemes for the multi-ac port type modular multi-level converter are as follows:
preferably, the first single-phase converter and the second single-phase converter in the MIM of the multi-ac port type modular multilevel converter have the same dc component of the output voltage, and the respective dc components may not be completely the same and adopt corresponding control and modulation strategies;
preferably, the dc component of the output voltage of each single-phase converter may be half of the voltage of the common dc bus, in order to fully exert the modulation capability of the ac component thereof, or any other dc component greater than zero and smaller than the voltage of the common dc bus may be used;
preferably, when the output voltages of the second single-phase converters in the scheme 3 of the multi-alternating-current port type modular multi-level converter are completely consistent, the scheme 3 can be equivalent to the topology structure of the scheme 2; in the scheme 3 of the multi-ac port type modular multilevel converter, when the ac component of the output voltage of the second single-phase converter connected to the upper bridge arm of the MMC is set to be zero, the dc component of the output voltage of the second single-phase converter connected to the lower bridge arm of the MMC is set to be the common dc bus voltage, and the ac and dc components of the output voltage of the second single-phase converter connected to the lower bridge arm of the MMC are both set to be zero, the scheme 3 can be equivalent to the topology structure of the scheme 1.
The invention also provides a flexible interconnection system between a multi-terminal alternating current line and a medium-high voltage direct current network by adopting the multi-alternating current port type modular multilevel converter, as shown in fig. 7 and 8, the core equipment of the multi-alternating current line type flexible interconnection system is the multi-alternating current port type modular multilevel converter, and the system further comprises an alternating current line, a direct current line, an alternating current load, a direct current load, an energy storage device and the like.
The multi-AC type port type modularized multi-level converter is arranged at the collection position of a plurality of AC lines and a medium-high voltage DC power grid, each AC line is connected with the MIM in the invention, and the medium-high voltage DC power grid is connected with the MMC DC side in the invention; each alternating current line can be connected with an alternating current load, can be connected with a direct current load or energy storage equipment through an AC/DC converter, can be connected with a low-voltage alternating current system through a step-down transformer, and can also be connected with a high-voltage alternating current system through a step-up transformer; the medium-high voltage direct current power grid can be connected with a high-capacity photovoltaic, can also be connected with a low-voltage direct current power grid through a buck converter, and can also be connected with a high-voltage direct current power transmission system through a boost converter.
Preferably, the multi ac line type flexible interconnection system may include a multi ac port type modular multi-level inverter, as shown in fig. 7; a plurality of multi-ac port type modular multilevel converters can also be included, as shown in fig. 8; when the multi-alternating current line type flexible interconnection system comprises two or more multi-alternating current port type modular multi-level converters, each multi-alternating current port type modular multi-level converter is installed at the collection position of a plurality of alternating current lines and a medium-high voltage direct current power grid in each region, and the regions are interconnected through a medium-high voltage direct current line on the direct current side of the MMC by using a DC/DC converter, so that an annular or mesh structure with a more complex topological structure and higher power supply reliability is formed.
Further, the invention provides an overvoltage protection method for a single-phase converter in a multi-ac port type modular multi-level converter, and the specific method is as shown in fig. 9, the protection method is realized by a protection device of the single-phase converter connected in parallel in the multi-ac port type modular multi-level converter, the protection device comprises a Metal-oxide Varistors (MOV) and a thyristor bypass switch connected in parallel with the MOV, and the thyristor bypass switch is formed by connecting a static resistor, a resistance-capacitance loop and an anti-parallel thyristor in parallel and then connecting a saturable reactor in series.
The MOV can limit the output voltage of the single-phase converter within a safe protection range, and when the output voltage of the first single-phase converter exceeds a safe and stable operation range, the thyristor bypass switch realizes overvoltage protection by bypassing the corresponding switch of the first single-phase converter.
Furthermore, the present invention provides a method for starting a multi ac port type modular multilevel converter, which can respectively comprise four stages:
the first stage is an uncontrolled charging stage, the alternating current circuit 1 is connected with a current-limiting resistor in series and is connected to the grid, all switches are locked, and alternating current network current charges a capacitor in the multi-alternating current port type modular multilevel converter through a freewheeling diode of each switch;
the second stage is a controlled charging stage, after the uncontrolled charging in the first stage is finished, the voltage of each capacitor does not reach a reference value, the number of the charging capacitors in the loop is constant in a switch alternate switching mode, and the voltage of the capacitor in the multi-alternating-current port type modular multilevel converter is further improved;
the third stage is a ramp boosting stage, after the charging of the second stage is finished, a voltage control loop is put into the charging process, a reference voltage adopting ramp change is given, and the voltage of each capacitor is charged to a reference value; a voltage control outer ring commonly used by a voltage control ring MMC and a common direct current bus voltage control ring in the second aspect of the invention, wherein when the voltage charging of a capacitor in the multi-alternating current port type modular multilevel converter is completed, the voltage control outer ring of the MMC is switched to a constant power control outer ring in the second aspect of the invention;
and the fourth stage is an alternating current circuit input stage, after the three stages are charged, the other alternating current circuits are matched with respective circuit current control rings and the reference given output of the first single-phase converter connected with the circuit current control rings to realize soft input.
Furthermore, the invention provides a control system suitable for the multi-ac port type modular multilevel converter, wherein the control system of the multi-ac port type modular multilevel converter can adopt a centralized control architecture, a distributed control architecture or a hybrid architecture; the centralized control architecture, namely alternating current circuit power flow control, related control in the MMC and common direct current bus voltage balance control are realized in the same controller, and the centralized control architecture is characterized by simple structure and less equipment; the distributed control architecture classifies all control links, and respectively places the control links in a plurality of controllers at the same level, if each alternating current power flow control, related control in an MMC and common direct current bus voltage balance control are respectively in three different controllers, the controllers at the same level independently operate, and the distributed control architecture is characterized by flexible configuration and rapid calculation; in addition, a layered hybrid control architecture combining centralized control and distributed control can be adopted, each control in the system is placed in a plurality of controllers of different levels according to a certain logical relationship, for example, each alternating current line power flow control, MMC power outer loop control and current inner loop control are in a first-level controller, reference voltage calculation, common direct current bus voltage balance control and the like of the first single-phase converter are respectively in a plurality of second-level controllers, information communication exists among the controllers of different levels, and information communication does not exist among the controllers of the same level. The controller is a hardware device with control capability, such as a controller based on a field programmable gate array chip, a controller based on a digital signal processing chip, and the like.
In summary, referring to fig. 4 to 6, the invention provides a multi-ac port type modular multilevel converter with active power flow control capability suitable for a medium-high voltage ac/dc hybrid power grid, and the multi-ac port type modular multilevel converter comprises a Modular Multilevel Converter (MMC) and a multi-port flexible interconnect module (MIM) connected with the MMC.
The modular multilevel converter is a medium-high voltage level voltage source type converter, adopts a modular cascade mode, and has remarkable advantages in the aspects of manufacturing difficulty, switching loss, waveform quality and the like; in addition, the device has the bidirectional flow function of active power, can absorb active power from a direct current system, and can also provide active power for the direct current system. The multi-port flexible interconnection module comprises a plurality of first single-phase converters which are mutually connected in parallel on the same common direct-current bus, and the output ports of the first single-phase converters are connected with an alternating-current line; by adjusting the amplitude phase of the alternating current component in the output voltage of the first single-phase converter connected with the line, active control of the alternating current line power flow can be realized. In addition, according to different connection modes of the multi-port flexible interconnection module and the modular multilevel converter, as shown in fig. 4 to 6, the multi-port flexible interconnection module may further include one or two second single-phase converters connected in parallel with the first single-phase converter. When the multi-terminal flexible interconnection module does not comprise a second single-phase converter, the alternating current ports of the upper bridge arm and the lower bridge arm of the modular multi-level converter are respectively connected with the positive pole and the negative pole of a common direct current bus in the multi-terminal flexible interconnection module, as shown in fig. 4; when the multi-terminal flexible interconnection module comprises a second single-phase converter, the output port of the second single-phase converter is connected with the alternating current output port of the modular multilevel converter, as shown in fig. 5; when the multi-terminal flexible interconnection module comprises two second single-phase converters, the output ports of the two second single-phase converters are respectively connected with the alternating current ports of the upper bridge arm and the lower bridge arm of the modular multilevel converter, as shown in fig. 6; in the topology shown in fig. 4, the energy balance of the multi-terminal flexible interconnect module is achieved by changing the ac component in the output voltage of the first single-phase converter connected to the ac line 1 and the modulation strategy of the modular multilevel converter; in the topologies shown in fig. 5 and 6, the stabilization of the system is achieved by changing the ac component in the output voltage of the second single-phase converter and the modulation strategy of the modular multilevel converter.
According to the invention, a multi-port flexible interconnection module (MIM) is innovatively introduced on the basis of a modular multilevel converter, a plurality of AC line feed-in ports are provided, the interconnection of a plurality of AC lines and a DC power grid in a station of the same converter station is realized, and the active control on the AC line power flow can be realized by adjusting the amplitude and the phase of the AC component of the output voltage of a first single-phase converter connected with the AC lines; compared with the existing common networking structure of the AC/DC converter station, namely the schemes a-c in the figure 2, the invention adopts a transformerless structure, adopts a mode of simultaneously feeding a plurality of AC lines and an AC/DC power grid interconnection mode, and has great advantages in the aspects of power density, converter station size, construction cost, power supply reliability, power supply system operation efficiency and the like; the flexible interconnection of the multiple alternating current lines is realized by utilizing the multi-terminal flexible interconnection module, the flexible interconnection has the characteristic of modularization, and the port expansion of the alternating current lines can be economically, efficiently and conveniently realized by increasing the number of the first single-phase converters in the interconnection module.
Example 2
Referring to fig. 10 to 19, in order to verify and explain technical effects adopted in the method, the present embodiment specifically describes a multi-ac port type modular multilevel converter with reference to two specific embodiments, and performs simulation on the above embodiments to verify validity and feasibility of power flow control and energy balance, and to verify a real effect of the method by a scientific demonstration.
The multi-ac port type modular multilevel converter is specifically described with reference to two specific embodiments:
(1) in a first embodiment, as shown in fig. 10, the present invention uses a multi-ac port type modular multi-level converter to interconnect two ac lines with a medium-high voltage dc network; the AC port type modular multilevel converter comprises a modular multilevel converter adopting a two-level half-bridge type converter and a multi-port flexible interconnection module connected with the modular multilevel converter. In this embodiment, the multi-port flexible interconnect module comprises two first single-phase converters and one second single-phase converter, both of which are two-level half-bridge inverters and share the same common dc bus with each other; two first single-phase converters are respectively connected with two alternating current lines, and a second single-phase converter is connected with an alternating current port of the modular multilevel converter; by adjusting the AC output voltage of the first single-phase converter connected with the line and the AC output voltage of the second single-phase converter connected with the modular multilevel converter, the active control of the power flow on the AC line is realized on the basis of realizing the internal energy balance of the multi-end flexible interconnection module.
For the double ac line interconnection system implemented by the multi ac port type modular multilevel converter shown in fig. 10, the energy balance of the two port type modular multilevel converter is expressed by the stability of the capacitor voltage between the common dc buses in the two-end flexible interconnection device and the capacitor voltage in the modular multilevel converter, that is, the active power flowing into the above-mentioned device is required to be constantly zero, that is:
Figure BDA0003134163460000281
the first line of the equation represents that the active power flowing into the multi-end flexible interconnection module is zero, and the second line of the equation represents that the active power flowing into the modular multilevel converter is zero;
Figure BDA0003134163460000282
vector expressions of the alternating current components in the output voltage of the first single-phase converter connected to the alternating current lines 1 and 2, respectively;
Figure BDA0003134163460000283
conjugate expressions of the ac current vectors on the ac lines 1, 2, respectively;
Figure BDA0003134163460000284
a vector representation of an AC component of an output voltage for a second single-phase converter connected to the modular multilevel converter;
Figure BDA0003134163460000285
is a conjugate expression of an alternating current vector flowing into an alternating current port of the modular multilevel converter; u shapedcThe voltage is the direct current side voltage of the modular multilevel converter; i isdcThe current flows out of the direct current side of the modular multilevel converter; by regulating
Figure BDA0003134163460000286
The amplitude and the phase of the modular multilevel converter and the modulation degree of the sub-modules of the modular multilevel converter make the above equation hold, that is, the energy balance of each part of the device of the two-port modular multilevel converter in the embodiment is realized.
(2) In a first embodiment, as shown in fig. 16, a modular multilevel converter of the multiple ac port type is used to interconnect three ac lines with a medium-high voltage dc network; the AC port type modular multilevel converter comprises a modular multilevel converter adopting a two-level half-bridge type converter and a multi-port flexible interconnection module connected with the modular multilevel converter. In this embodiment, the multi-port flexible interconnect module comprises three first single-phase converters and one second single-phase converter, which are two-level half-bridge inverters and share the same common dc bus with each other; three first single-phase converters are connected to three ac lines respectively and a second single-phase converter is connected to an ac port of the modular multilevel converter. In this embodiment, the principle of achieving internal energy balance of the multi-port flexible ac interconnection device is the same as that described in (1).
The above embodiments are simulated by using MATLAB/Simulink software to verify the effectiveness and feasibility of power flow control and energy balance, and the simulation parameters are shown in table 1.
Table 1: and (4) a simulation parameter table.
Parameter(s) Numerical value
Rated apparent power of line SN＝1MV·A
Line 1 voltage V1line,rms＝10.5kV,θ1＝0°
Line 1 impedance L1＝35mH,R1＝0.55Ω
Line
2 voltage V2line,rms＝10.5kV,θ2＝-3°
Line 2 impedance L2＝35mH,R2＝0.55Ω
Line
3 voltage V1line,rms＝10.5kV,θ3＝-6°
Line 3 impedance L3＝35mH,R3＝0.55Ω
MIM common connection capacitor Clink＝4mF,Vlink＝2500V
MMC submoduleCapacitor with a capacitor element C＝2mF,VC＝1750V
MMC sub-module number 12 (Single arm)
Switching frequency 1kHz
Simulation example one:
in the first embodiment, a schematic diagram of system wiring for interconnecting two ac lines and a dc grid by using a multi-ac port type modular multilevel converter is shown in fig. 10, and a corresponding control method is shown in fig. 11; the two-AC port type modular multilevel converter comprises three half-bridge type converters, wherein the two half-bridge type converters connected with an AC line control the active power and the reactive power on a control line 2 through a line current; the half-bridge type converter connected with the modular multilevel converter ensures the stability of the voltage of the public connection capacitor through the voltage control of the public direct current bus; the reactive power on the ac line 1 and the power on the dc side of the modular multilevel converter can be regulated by the outer loop power control of the modular multilevel converter.
In the first embodiment, four different operation conditions are set in a simulation mode to verify the effectiveness of active power flow control of the multi-alternating-current port type modular multilevel converter; furthermore, in view of the simplicity of the calculation, the ac output voltage of the first single-phase converter is distributed equally, i.e.
Figure BDA0003134163460000301
The reference values of the following per unit values are the rated apparent power S of the modular multilevel converterN＝2MV·A。
Table 2: four different operation condition experiment parameter tables.
PL/p.u. Q1/p.u. P2/p.u. Q2/p.u.
Working condition 1 0.8 0.3 0.4 0.2
Working condition 2 0.3 -0.2 0.2 -0.2
Working condition 3 -0.3 -0.1 -0.15 -0.2
Working condition 4 -0.8 0.3 -0.4 0.3
In the working condition 1, the direct current line runs in a heavy load mode, active power flows from the alternating current side to the direct current side, and the two alternating current lines distribute the active power averagely; in working condition 2, the direct current line runs under light load, active power flows from the alternating current side to the direct current side, and the line 2 bears more active power; in working condition 3, the direct-current line runs under light load, active power flows from the direct-current side to the alternating-current side, and the two alternating-current lines averagely distribute the active power; in working condition 4, the medium-high voltage direct current line operates under heavy load, active power flows from the direct current side to the alternating current side, and the line 2 absorbs more active power.
FIGS. 12 to 15 are simulation results from working condition one to working condition four in the first embodiment, respectively, each graph includes 8 waveform diagrams, and the active power P at the DC side of the MMC is sequentially set according to the sequenceLWave form diagram, line 1 active power P1And reactive power Q1Oscillogram, line 2 active power P2And reactive power Q2Oscillogram, three-phase common DC bus voltage Vlink_abcOscillogram, three-phase MMC sub-module capacitance voltage Vcapacitor_abcOscillogram (MMC upper bridge arm), line 1 three-phase current i1abcOscillogram, line 2 three-phase current i2abcOscillogram and direct current I flowing out of MMCdcAnd (4) waveform diagrams.
Simulation waveform results show that the multi-alternating-current port type modular multilevel converter can ensure the stable operation of a system and can realize the active control of alternating-current line power flow and MMC direct-current side power.
Simulation example two:
in the second embodiment, a schematic diagram of system wiring for interconnecting three ac lines and a medium-high voltage dc power grid by using a multi-ac port type modular multilevel converter is shown in fig. 16, and a corresponding control method is shown in fig. 17; the three-AC port type modular multilevel converter comprises five half-bridge type converters, wherein the three half-bridge type converters connected with an AC line control active power and reactive power on control lines 2 and 3 through line tide current; the two half-bridge type converters connected with the modular multilevel converter ensure the stability of the voltage of the public connection capacitor through the voltage control of the public direct current bus; the reactive power on the ac line 1 and the power on the dc side of the modular multilevel converter can be regulated by the outer loop power control of the modular multilevel converter.
Unlike the above-described embodiments, the method for distributing the ac output voltages of the first single-phase converter in the second embodiment adopts the optimal distribution method mentioned in the present invention: the maximum value of the amplitude of the AC output voltage of each single-phase converter being minimal, i.e.
Figure BDA0003134163460000311
At a minimum, the injected circulating current component is minimized on the basis of the minimum, so that an AC output voltage reference value of a first single-phase converter connected with the line 1 is obtained
Figure BDA0003134163460000312
In the second embodiment, the set simulation conditions are as follows: the medium-high voltage direct current line runs in a heavy load mode, active power flows from the alternating current side to the direct current side, and the active power is distributed to the three alternating current lines in an average mode; in particular, PL＝0.45p.u.，Q1＝0.2p.u.，P2＝0.15p.u.，Q2＝0.2p.u.，P3＝0.15p.u.，Q20.2 p.u.; the reference values of the per unit values are the rated apparent power S of the modular multilevel converterN＝3MV·A。
FIGS. 18 to 19 are simulation results of the second embodiment, which totally include 10 oscillograms, and sequentially include the active power P at the DC side of the MMC according to the sequenceLWave form diagram, line 1 active power P1And reactive power Q1Oscillogram, line 2 active power P2And reactive power Q2Wave diagram, line 3 active power P3And reactive power Q3Oscillogram, three-phase common DC bus voltage Vlink_abcOscillogram, three-phase MMC sub-module capacitance voltage Vcapacitor_abcOscillogram (MMC upper bridge arm), line 1 three-phase current i1abcOscillogram, line 2 three-phase current i2abcOscillogram, line 3 three-phase current i3abcOscillogram and direct current I flowing out of MMCdcAnd (4) waveform diagrams.
Simulation waveform results show that the multi-alternating current port type modular multi-level converter can still realize active control of alternating current line power flow and MMC direct current side power while ensuring stable operation of a system on the basis of interconnecting three alternating current lines and a medium-high voltage direct current line, and simultaneously shows that the multi-alternating current port type modular multi-level converter has the capability of port expansion.
It should be noted that the above-mentioned embodiments are only for illustrating the technical solutions of the present invention and not for limiting, and although the present invention has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, which should be covered by the claims of the present invention.

Claims (21)

1. A multi ac port modular multilevel converter, comprising:
a modular multilevel converter; and the number of the first and second groups,
a multi-port flexible interconnect module in series with the modular multilevel converter.
2. The multi ac port modular multilevel converter of claim 1, wherein: the modular multilevel converter comprises a medium-high voltage level voltage source type converter.
3. The multi ac port modular multilevel converter of claim 1, wherein: the multi-port flexible interconnection module comprises a plurality of first single-phase converters connected in parallel on a common connecting bus, and an alternating current output port of each single-phase converter is connected with a corresponding alternating current line.
4. The multi ac port modular multilevel converter according to claim 1 or 2, wherein: the modular multilevel converter submodule topology comprises a half-bridge submodule topology, a full-bridge submodule topology, a clamping type dual-submodule topology or a topology formed by multiple structures in a mixed connection mode.
5. The multi ac port modular multilevel converter of claim 3, wherein: the common connection bus comprises a medium and low voltage direct current bus, and a common connection capacitor connected with the medium and low voltage direct current bus provides voltage for the medium and low voltage direct current bus.
6. The multi ac port modular multilevel converter according to any of claims 1, 3, 5, wherein: the multi-port flexible interconnection module is divided into three schemes according to the fact whether a second single-phase converter is included or not and the difference of the wiring modes of the included second single-phase converter and the modular multi-level converter upper and lower bridge arms, and comprises,
scheme 1: the multi-port flexible interconnection module does not comprise the second single-phase converter, and alternating current output ports of an upper bridge arm and a lower bridge arm of the modular multi-level converter are respectively connected with a positive pole and a negative pole of a common direct current bus of the multi-port flexible interconnection module;
scheme 2: the multi-port flexible interconnection module comprises a second single-phase converter which is connected with the first single-phase converter in parallel at two ends of a common direct-current bus, and an alternating-current port of the modular multilevel converter is connected with an alternating-current output port of the second single-phase converter;
scheme 3: the flexible interconnection module of multiport contains first single-phase transverter and two single-phase transverters of second with alternating current line quantity matching, first single-phase transverter and two single-phase transverters of second connect in parallel at public direct current bus both ends, the AC output port of two single-phase transverters of second respectively with the AC output port of the upper and lower bridge arm of modularization multi-level transverter links to each other.
7. The multi ac port modular multilevel converter of claim 6, wherein: the first single-phase converter and the second single-phase converter comprise voltage source type single-phase converters.
8. The multi ac port modular multilevel converter of claim 7, wherein: the topology of the first single-phase converter or the second single-phase converter in the multi-port flexible interconnection module comprises a two-level half-bridge converter, a three-level half-bridge converter or a single-phase bridge converter capable of performing power bidirectional flow.
9. The multi ac port modular multilevel converter of claim 8, wherein: the output voltage of a port of a single-phase converter in the multi-terminal flexible interconnection module comprises direct current components with the same size and different alternating current components obtained by control according to requirements;
and the direct-current component of the voltage of the output port of the single-phase converter is half of the voltage value of the public connection bus.
10. A control method applied to the multi ac port modular multilevel converter according to claim 1, wherein: the method comprises alternating current line power flow control, modular multilevel converter control and common direct current bus voltage balance control.
11. The method of controlling a multiple ac port modular multilevel converter of claim 10, wherein: also comprises the following steps of (1) preparing,
the multi-end flexible interconnection module and the modular multilevel converter flexibly interconnect a plurality of alternating current lines and a direct current power grid through cooperative control, and adjust the power flow distribution on the lines;
when the multi-section flexible interconnection module is interconnected with n AC lines, the power flow P on each AC line is adjusted1～PnAnd Q1～QnAnd DC side load power PLControl is carried out, wherein the active power of one AC line is automatically adjusted through the energy balance of the system, and only the reactive power on the line is adjustedControlling the rate, and defining the AC line as an AC line 1;
in the control, the three-phase alternating current component locked by the phase-locked loop is the three-phase node voltage of the alternating current line 1 controlled by the constant reactive power, and the voltage current under the three-phase alternating current a-b-c coordinate system is converted into a d-q coordinate system through Park conversion for active and reactive component decoupling control through the phase of the real-time output power grid voltage.
12. The method for controlling a multiple ac port modular multilevel converter according to claim 10 or 11, wherein: the ac line power flow control comprises,
voltage v at node 1 of column write line based on AC line 11jNode voltage v to line kkjAnd converting the dynamic equation into a d-q coordinate system to obtain the following equation:
Figure FDA0003134163450000031
wherein, V1d、V1q、Vkd、Vkq、I1d、I1q、Ikd、IkqD-q axis components, L, of line 1 and line k node voltage currents, respectively1、R1、Lk、RkThe inductance and the equivalent resistance on the line 1 and the line k respectively, omega represents the angular frequency of the power grid, delta Uc1kd、ΔUc1kdIs an equivalent voltage Deltauc1kj＝uc1j-uckjD-q axis component of (u)c1jIs the AC component of the output voltage of a first single-phase converter connected to an AC line 1ckjJ is a, b, c, an ac component of the output voltage of the first single-phase converter connected to the ac line k.
13. The method of controlling a multiple ac port modular multilevel converter of claim 12, wherein: also comprises the following steps of (1) preparing,
and performing closed-loop control on the current on the line k by using a PI controller, wherein a specific control equation is as follows:
Figure FDA0003134163450000032
wherein the superscripts denote reference values, k, of the respective componentspkAnd kikProportional and integral coefficients, V, of a power flow control loop PI regulator of line k, respectively1d、V1q、Vkd、VkqFor the feed-forward term,. omega.L1I1d、ωL1I1q、ωLkIkd、ωLkIkqIs a feedforward decoupling term;
a d-axis component reference value of a line current of the AC line power flow control loop
Figure FDA0003134163450000033
And q-axis component reference value
Figure FDA0003134163450000034
Reference value of active power according to ac line k
Figure FDA0003134163450000035
And a reactive power reference value
Figure FDA0003134163450000036
And calculating to obtain:
Figure FDA0003134163450000037
14. the method for controlling a multiple ac port modular multilevel converter according to claim 10 or 11, wherein: the modular multilevel converter control comprises that,
when the MIM in the multi-AC port type modular multi-level converter only comprises one second single-phase converter, a mathematical model of the currents of the MMC AC port and the upper and lower bridge arms is established, and Park is carried out to convert the mathematical model into a d-q coordinate system which rotates synchronously with the AC line 1, so that the current of the MMC AC port is obtained:
Figure FDA0003134163450000038
wherein, Uod、Uoq、Iod、IoqRespectively the voltage u at the AC port of the MMCojAnd current iojD-q axis component of (1), Δ Vd、ΔVqRespectively MMC equivalent voltage Deltavj＝(unj-upj) D-q axis component of/2, upj、unjRespectively, an upper bridge arm equivalent voltage and a lower bridge arm equivalent voltage of MMC, L0、R0The bridge arm inductance L and the bridge arm resistance R are half of those of the MMC respectively, and j is a, b and c;
MMC alternating side current i by utilizing PI controllerojAnd performing closed-loop control, wherein a specific control equation is as follows:
Figure FDA0003134163450000041
wherein the superscripts denote reference values, k, of the respective componentspoAnd kioProportional and integral regulation coefficients, U, of a PI regulator in MMC current inner loop control, respectivelyod、UoqIs an MMC alternating-current port voltage disturbance suppression item for enhancing the anti-interference capability of a control loop, omega L0Iod、ωL0IoqIs a feedforward decoupling term;
the MMC has an active current reference value
Figure FDA0003134163450000042
Reference value of reactive current
Figure FDA0003134163450000043
Reference value of reactive power
Figure FDA0003134163450000044
The calculation expression of (a) is as follows:
Figure FDA0003134163450000045
15. the method of controlling a multiple ac port modular multilevel converter of claim 14, wherein: also comprises the following steps of (1) preparing,
when the second single-phase converter is not included or two second single-phase converters are included in the MIM in the multi-ac port type modular multilevel converter, the current i at the MMC ac portojThe sum of the currents of the AC lines is:
Figure FDA0003134163450000046
16. the method of controlling a multiple ac port modular multilevel converter of claim 14, wherein: also comprises the following steps of (1) preparing,
when the MIM adopts the structure of scheme 2, the modulation wave of the upper bridge arm of the MMC
Figure FDA0003134163450000047
Modulated wave of lower bridge arm
Figure FDA0003134163450000048
The computational expressions included are as follows:
Figure FDA0003134163450000049
when the MIM adopts the structure of scheme 1, the modulation wave of the upper bridge arm of the MMC
Figure FDA0003134163450000051
Modulated wave of lower bridge arm
Figure FDA0003134163450000052
The computational expressions included are as follows:
Figure FDA0003134163450000053
when the MIM adopts the structure of scheme 3, the modulation wave of the upper bridge arm of the MMC
Figure FDA0003134163450000054
Modulated wave of lower bridge arm
Figure FDA0003134163450000055
The computational expressions included are as follows:
Figure FDA0003134163450000056
wherein,
Figure FDA0003134163450000057
fundamental frequency circulating current injected in an MMC bridge arm for controlling MIM energy balance and MMC upper and lower bridge arm energy balance.
17. The method for controlling a multiple ac port modular multilevel converter according to claim 10 or 11, wherein: the common dc bus voltage balance control includes,
when the MIM employs the topology of scheme 1, the control equation is as follows:
Figure FDA0003134163450000058
wherein, Vlinka、Vlinkb、VlinkcIs a three-phase common dc bus voltage,
Figure FDA0003134163450000059
three-phase reference voltage, k, for feed-forwardp1、ki1Respectively is a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller in the scheme;
the reference voltages are:
Figure FDA00031341634500000510
wherein,
Figure FDA00031341634500000511
the reference voltage is j-phase modulated for the first single-phase converter connected to the ac line 1,
Figure FDA00031341634500000512
j-phase modulation of a reference voltage, V, for a first single-phase converter connected to an AC line kcommon,dcA reference value of a DC component common to the first single-phase converter and the second single-phase converter, the reference value being greater than zero and less than the common DC bus voltage
Figure FDA00031341634500000513
When the MIM employs the topology of scheme 2, the control equation is as follows:
Figure FDA0003134163450000061
wherein k isp2、ki2Respectively a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller, and the feedforward term is 0;
the modulation reference voltage of each of the first single-phase converter and the second single-phase converter is as follows:
Figure FDA0003134163450000062
when the MIM employs the topology of scheme 3, the control equation is as follows:
Figure FDA0003134163450000063
wherein k isp3、ki3Respectively is a proportional link gain coefficient and an integral link gain coefficient of the proportional integral controller in the scheme;
the modulation reference voltage of each of the first single-phase converter and the second single-phase converter is as follows:
Figure FDA0003134163450000064
wherein,
Figure FDA0003134163450000065
the reference voltage is a three-phase reference voltage j alternating current reference voltage of a second single-phase converter connected with an upper bridge arm of the MMC.
18. The method of controlling a multiple ac port modular multilevel converter of claim 17, wherein: the basic condition equations required to be met by the distribution mode of the alternating-current equivalent voltages of the first single-phase converter and the second single-phase converter comprise,
when the MIM adopts the topology of scheme 1, the equivalent alternating current component of the output voltage of the first single-phase converter and the line current satisfy the following relation:
Figure FDA0003134163450000066
wherein,
Figure FDA0003134163450000071
is a vector representation of the ac component of the output voltage of the first single-phase converter connected to the ac line 1,
Figure FDA0003134163450000072
outputting a vector representation of the AC component of the voltage for a first single-phase converter of said multi AC port type modular multilevel converter connected to an AC line k,
Figure FDA0003134163450000073
a vector expression of a series equivalent voltage AC component between the AC line 1 and the AC line k required for the purpose of performing the target power flow control for the AC line k,
Figure FDA0003134163450000074
expressed as the conjugate of the AC current vector on line k, VlinkVoltage magnitude between common DC buses in MIM for multi-AC port modular multilevel converter, IdcThe method comprises the steps that MMC current flows out of the direct current side of the multi-alternating current port type modular multi-level converter, and n is the number of alternating current lines which are interconnected with each other at the alternating current side of the multi-alternating current port type modular multi-level converter;
when the MIM adopts the topology of scheme 2, the line current of each first single-phase converter and each second single-phase converter meets the following basic conditions:
Figure FDA0003134163450000075
wherein,
Figure FDA0003134163450000076
is a vector expression of the equivalent voltage alternating current component of the second single-phase converter connected with the MMC,
Figure FDA0003134163450000077
for flowing into MMCA conjugate expression of an alternating current vector of a flow port;
when the MIM adopts the topology of scheme 3, the line current of each first single-phase converter and each second single-phase converter and the injected fundamental frequency circulating current meet the following basic conditions:
Figure FDA0003134163450000078
wherein,
Figure FDA0003134163450000079
is a vector expression of the equivalent voltage alternating current component of the second single-phase current converter connected with the upper bridge arm and the lower bridge arm of the MMC,
Figure FDA00031341634500000710
for a conjugate expression of the sum of the ac line current vectors,
Figure FDA00031341634500000711
is a conjugate expression of the injected fundamental circulating current.
19. The method of controlling a multiple ac port modular multilevel converter of claim 18, wherein: the first single-phase converter and the second single-phase converter have distribution mode of alternating-current equivalent voltage
Figure FDA00031341634500000712
The selection of (a) includes that,
the distribution mode of the multi-end flexible interconnection module for connecting equivalent voltage in series on the distribution network feeder line is as follows:
Figure FDA00031341634500000713
in the case of MIM employing scheme 1,
Figure FDA00031341634500000714
a feed-forward term for the output voltage of the single-phase converter connected in series with the line 1;
the above-mentioned
Figure FDA0003134163450000081
The maximum value of the amplitude of the alternating current component of the output voltage of each first single-phase converter and each second single-phase converter is the minimum:
when the MIM adopts the topology of scheme 1, the
Figure FDA0003134163450000082
Is selected to satisfy
Figure FDA0003134163450000083
Taking the minimum value;
when the MIM adopts the topology of scheme 2, the
Figure FDA0003134163450000084
Is selected to satisfy
Figure FDA0003134163450000085
Taking the minimum value;
when the MIM adopts the topology of scheme 3, the
Figure FDA0003134163450000086
Is selected to satisfy
Figure FDA0003134163450000087
Taking the minimum value.
20. The method of controlling a multiple ac port modular multilevel converter according to claim 18 or 19, wherein: the overvoltage protection strategy of the voltage of the multi-alternating current port type modular multi-level converter connected in series on the feeder line comprises the following steps,
a protection device is connected in parallel between the alternating current output ports of the first single-phase current converter in the multi-terminal flexible interconnection module;
the protection device is formed by connecting a metal oxide voltage limiter and a thyristor bypass switch in parallel, the metal oxide voltage limiter limits the voltage at a protection level, and the thyristor bypass switch bypasses an alternating current output port of the first single-phase converter;
the thyristor bypass switch is formed by connecting an anti-parallel thyristor, a resistance-capacitance loop and a static resistor in parallel and then connecting the thyristor bypass switch with a saturable reactor in series.
21. The method of controlling a multiple ac port modular multilevel converter of claim 20, wherein: the starting strategy of the multi-AC port type modular multilevel converter comprises the following steps,
the first stage is as follows: in the uncontrolled charging stage, the alternating current circuit 1 is connected with a current-limiting resistor in series and is connected to the grid, all switches are locked, and the current of the alternating current grid charges a capacitor in the multi-alternating current port type modular multilevel converter through a freewheeling diode of each switch;
and a second stage: in the controlled charging stage, after the uncontrolled charging in the first stage is finished, the voltage of each capacitor does not reach a reference value, the number of the charged capacitors in a loop is constant in a switch alternate switching mode, and the voltage of the capacitor in the multi-alternating-current port type modular multilevel converter is further improved;
and a third stage: a ramp boosting stage, after the charging in the second stage is finished, putting a voltage control loop and giving a reference voltage adopting ramp change, and charging the voltage of each capacitor to a reference value;
a fourth stage: and in the input stage of the alternating current circuit, after charging is completed, the other alternating current circuits are matched with respective circuit current control rings and the reference given output of the first single-phase converter connected with the circuit current control rings to realize soft input.
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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114069595A (en) * 2021-12-02 2022-02-18 上海交通大学 Direct-current transformer system with direct-current power flow control function and control method thereof
CN114070115A (en) * 2021-11-24 2022-02-18 上海交通大学 Multi-alternating-current-port high-voltage direct-hanging energy storage power conversion system and control method thereof
CN114285066A (en) * 2021-12-28 2022-04-05 国网北京市电力公司 Power balance coordination control method and system for multi-terminal flexible interconnection power distribution system
CN114499251A (en) * 2022-01-29 2022-05-13 清华大学 Converter system and control method thereof
CN114530885A (en) * 2022-02-28 2022-05-24 国网江苏省电力有限公司丹阳市供电分公司 Network-building type flexible interconnection device and control method thereof
CN114598175A (en) * 2022-03-18 2022-06-07 国网智能电网研究院有限公司 Energy balance control device based on multi-port modular multilevel DC transformer
CN116581790A (en) * 2023-07-12 2023-08-11 广东电网有限责任公司佛山供电局 Method and system for restraining modularized multi-level converter in unbalanced power grid
US11764703B1 (en) * 2022-08-22 2023-09-19 Foshan Hechu Energy Technology Co., Ltd. Power conversion method for alternating current direct grid-connected type battery energy storage system
CN117293888A (en) * 2023-09-27 2023-12-26 国网湖北省电力有限公司随州供电公司 Weak current network low voltage treatment method based on back-to-back modularized multi-level converter
WO2024040876A1 (en) * 2022-08-26 2024-02-29 上海交通大学 Transformer-lessgeneralized unified power flow controller, method, and system
CN114530885B (en) * 2022-02-28 2024-07-26 国网江苏省电力有限公司丹阳市供电分公司 Net-structured flexible interconnection device and control method thereof

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102904420A (en) * 2012-09-29 2013-01-30 中国科学院电工研究所 Multi-port current transformer
CN107134926A (en) * 2017-04-20 2017-09-05 清华大学 A kind of modular electric energy router combinational circuit
US20190199096A1 (en) * 2017-12-21 2019-06-27 The Governors Of The University Of Alberta Multi-terminal modular dc-dc converter for dc networks
CN112510715A (en) * 2020-10-31 2021-03-16 上海交通大学 Multi-port alternating current power grid flexible interconnection device and control method and system thereof
CN112736977A (en) * 2020-12-31 2021-04-30 中国长江三峡集团有限公司 Multi-terminal offshore wind power flexible direct current and energy storage cooperative grid-connected system and control method thereof

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN102904420A (en) * 2012-09-29 2013-01-30 中国科学院电工研究所 Multi-port current transformer
CN107134926A (en) * 2017-04-20 2017-09-05 清华大学 A kind of modular electric energy router combinational circuit
US20190199096A1 (en) * 2017-12-21 2019-06-27 The Governors Of The University Of Alberta Multi-terminal modular dc-dc converter for dc networks
CN112510715A (en) * 2020-10-31 2021-03-16 上海交通大学 Multi-port alternating current power grid flexible interconnection device and control method and system thereof
CN112736977A (en) * 2020-12-31 2021-04-30 中国长江三峡集团有限公司 Multi-terminal offshore wind power flexible direct current and energy storage cooperative grid-connected system and control method thereof

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN114070115A (en) * 2021-11-24 2022-02-18 上海交通大学 Multi-alternating-current-port high-voltage direct-hanging energy storage power conversion system and control method thereof
CN114069595A (en) * 2021-12-02 2022-02-18 上海交通大学 Direct-current transformer system with direct-current power flow control function and control method thereof
CN114069595B (en) * 2021-12-02 2024-06-07 上海交通大学 DC transformer system with DC power flow control and control method thereof
CN114285066B (en) * 2021-12-28 2024-02-20 国网北京市电力公司 Power balance coordination control method and system for multi-terminal flexible interconnection power distribution system
CN114285066A (en) * 2021-12-28 2022-04-05 国网北京市电力公司 Power balance coordination control method and system for multi-terminal flexible interconnection power distribution system
CN114499251A (en) * 2022-01-29 2022-05-13 清华大学 Converter system and control method thereof
CN114530885A (en) * 2022-02-28 2022-05-24 国网江苏省电力有限公司丹阳市供电分公司 Network-building type flexible interconnection device and control method thereof
CN114530885B (en) * 2022-02-28 2024-07-26 国网江苏省电力有限公司丹阳市供电分公司 Net-structured flexible interconnection device and control method thereof
CN114598175A (en) * 2022-03-18 2022-06-07 国网智能电网研究院有限公司 Energy balance control device based on multi-port modular multilevel DC transformer
US11764703B1 (en) * 2022-08-22 2023-09-19 Foshan Hechu Energy Technology Co., Ltd. Power conversion method for alternating current direct grid-connected type battery energy storage system
WO2024040876A1 (en) * 2022-08-26 2024-02-29 上海交通大学 Transformer-lessgeneralized unified power flow controller, method, and system
CN116581790A (en) * 2023-07-12 2023-08-11 广东电网有限责任公司佛山供电局 Method and system for restraining modularized multi-level converter in unbalanced power grid
CN116581790B (en) * 2023-07-12 2024-02-27 广东电网有限责任公司佛山供电局 Method and system for restraining modularized multi-level converter in unbalanced power grid
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CN117293888B (en) * 2023-09-27 2024-05-24 国网湖北省电力有限公司随州供电公司 Weak current network low voltage treatment method based on back-to-back modularized multi-level converter

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